Investigation of loading and release in PVA-based hydrogels

We used Methylene Blue (MB) and Methyl Orange (MO) as model drugs to investigate the controlled release behavior of hydrogels from poly(vinvl alcohol) crosslinked with ethylenediaminetetraacetic dianhydride. The cationic or anionic character of these compounds and the molecular weight between crosslinks of the hydrogel and the concentration of ionizable groups in the hydrogel greatly affected the loading and release of the drugs. MB loading was favored, therefore, by a higher content of negative charges in the hydrogel, although this implied a greater degree of crosslinking and, therefore, a lower mesh size. On the other hand, the overall loading of negative MO, favored by a higher mesh size, was very low because of unfavorable interactions with the electrolyte charges. Release studies showed that one of the parameters that most affected the drug release behavior of these hydrogels was the pH of the solution. MB and MO were not completely released, even at pH 1. (C) 2002 Wiley Periodicals, Inc.